In motor vehicles with automatic or automated starting elements, starting processes produce drive situations in which, if the drive-train concerned is unsuitably regulated, uncomfortable conditions in the form of undesired rolling of the vehicle can occur. Whereas in drive-trains with hydrodynamic torque converters as the starting element, by virtue of their mode of operation, after a brake has been released crawling of the motor vehicle in the travel direction predetermined in each case takes place automatically, with starting elements in the form of separator clutches this can only happen by virtue of appropriate regulation of the separator clutch concerned. Thus, in drive-trains having automatic or automated separator clutches, assistance functions are often implemented, by means of which a hill start is facilitated for the vehicle driver in that, by virtue of the function, when actuation of a brake pedal has ended and until sufficient torque has been built up, an undesired rolling of the motor vehicle is prevented.
In most cases, when the motor vehicle concerned comes to rest, the braking pressure in the brake system is maintained and not reduced when the vehicle's driver reduces the actuation of the brake pedal. Usually, the braking pressure is only reduced when it is recognized, or it can be assumed that the motor vehicle can be held by a sufficient drive torque, or after a specified waiting time has elapsed. With regards to sufficient drive torque, either a corresponding measurement of the torque or an interrogation is made by one of the control units, such as the transmission control unit, or it is assumed that in the drive-train, after the passage of a certain time-period after the end of the brake actuation, a sufficient torque will be available. Sometimes, however, undesired rolling of the motor vehicle in the direction contrary to the predetermined travel direction is prevented by appropriate regulation of the starting element.
For example, EP 1 630 054 A1 describes a method for regulating a drive-train of a motor vehicle, in which by appropriate actuation of a starting element the motor vehicle concerned is electronically prevented from rolling. In the context of that method, as the specifications by a driver of the vehicle a predetermined travel direction, the reception of a command to release a brake of the motor vehicle, and the reception of a drive command are monitored. If then a starting situation of the motor vehicle is recognized, i.e. the brake release command has been given, but no drive command from the vehicle's driver has yet been received, then by virtue of a holding operation the motor vehicle is prevented from rolling in a direction contrary to the predetermined travel direction, in that if movement contrary to the predetermined travel direction is detected, then from the acceleration and the weight of the vehicle a necessary holding torque is calculated and the corresponding torque is called for from a drive engine of the motor vehicle. Furthermore, actuation of the starting element is corrected in such manner that the holding torque can be transmitted. Consequently, undesired rolling of the motor vehicle contrary to the predetermined travel direction is prevented.